A well known structure of amorphous silicon (a-Si) solar cells having a p-i-n junction is one employing amorphous silicon carbide (a-SiC) as the p-layer. In general, p-type a-SiC is obtained by the glow discharge decomposition of a mixed gas comprising silane gas (SiH.sub.4), methane gas (CH.sub.4), hydrogen (H.sub.2), and diborane gas (B.sub.2 H.sub.6). Recently, p-type silicon carbide (SIC) having a low resistivity and a wide optical forbidden band width or optical band gap (hereinafter referred to as E.sub.opt) has been developed as described in, for example, Technical Digest of the International PVSEC-3, 1987, pp. 49-52 and JP-A-64-42120. (The term "JP-A" as used herein means an unexamined published Japanese patent application.)
The method described in the former reference uses a hydrogen dilution ratio of 70 times or higher and a high-frequency power density as high as 260 mW/cm.sup.2 to form p-type SiC having an E.sub.opt of about 2.2 eV and an electric conductivity of about 1.times.10.sup.-2 (.OMEGA..cm).sup.-1. The method of the latter reference uses a hydrogen dilution ratio as high as about 500 times and a high-frequency power density as high as from 300 mW/cm.sup.2 to 1.5 W/cm.sup.2 to form p-type SiC having an E.sub.opt of about 2.1 eV and an electric conductivity of about 1.times.10.degree. (.OMEGA..cm).sup.-1.
However, the aforementioned methods for p-type SiC production, which employ CH.sub.4 as a carbon source, are disadvantageous in that they necessitate a high hydrogen dilution ratio and a high power density as described above since the addition of a large proportion of CH.sub.4 causes an abrupt decrease in electric conductivity and impairs film quality. In order to heighten the efficiency of solar cells, it is necessary to develop p-type SiC having a still higher E.sub.opt and a high electric conductivity. For use in larger-area solar cells, the SiC is required to be produced using a lower high-frequency power and have a lower resistivity even in a thin film form because the p-layer thickness is as small as 100 to 200 .ANG..